This invention relates to a droplet ejection apparatus that ejects liquid supplied from sub-tanks as droplets. Particularly, this invention is effective when applied to an inkjet recording apparatus (inkjet printer).
An ejection head of an inkjet recording apparatus or a droplet ejection apparatus ejects liquid, such as ink, in the form of droplets by use of a pressure means, such as piezo elements. When there are small holes, for example droplet ejection nozzles, on an ejection head, liquid which exists in the outlet of the droplet ejection nozzle becomes a dome-like shape and forms meniscus by the surface tension of the liquid.
Meanwhile, in a droplet ejection apparatus, when the ejection head is not in a state to eject droplets, that is, in a standby state wherein liquid is not pressed by the pressure means, such as piezo elements, liquid in the outlet of the droplet ejection nozzle should form meniscus curved toward inside of the droplet ejection nozzle by the surface tension of the liquid and the meniscus needs to be maintained in this shape.
However, since inside of the droplet ejection nozzle is filled with liquid, liquid in the droplet ejection nozzle usually tends to form meniscus projecting from the outlet of the droplet ejection nozzle due to the inner pressure (liquid pressure).
On the other hand, in a conventional inkjet recording apparatus, a porous absorber, which absorbs ink, is provided in a sub-tank. By an absorber aspirating liquid in the vicinity of the outlet of a droplet ejection nozzle, meniscus, curved toward inside of the droplet ejection nozzle, are maintained when the apparatus is in a standby state.
When droplets (ink) are ejected from an ejection head and consumed, liquid tends to move toward the ejection head. However, since liquid inside of a sub-tank is absorbed (impregnated) in an absorber and held therein, the liquid inside of a sub-tank cannot move freely as compared to a case wherein an absorber is not provided in a sub-tank.
Consequently, when droplets are ejected and ink (liquid) inside of a sub-tank is consumed, unevenness is caused in the amount of liquid held in different portions of an absorber, that is, in a portion of the absorber in vicinity of an ejection head and in a portion away from the ejection head.
When, for example, unevenness is caused, wherein large amount of liquid is held in a portion in vicinity of a liquid supply opening for replenishment, the absorber cannot reabsorb sufficient amount of liquid even when liquid is replenished (supplied) from the liquid supplying opening because large amount of liquid has been already absorbed (impregnated) in this portion of the absorber.
Therefore, in the above conventional inkjet recording apparatus, sufficient amount of ink (liquid) cannot be replenished, and the effectiveness in ink replenishment is low. The apparatus has a problem that ink inside of a sub-tank is consumed in a short time.